This invention relates in general to electrical submersible pump assemblies, and in particular, to an electrical submersible pump supported on coiled tubing with a feature to dislodge sand buildup from around the pump.
Electrical submersible pumps for oilwells typically include a centrifugal pump mounted to a downhole electrical motor. In a conventional installation, the upper end of the pump secures to a lower end of a string of production tubing. The production tubing comprises threaded sections of tubing secured together, each about 30 feet long. The motor usually locates below the pump. exterior of the tubing. The tubing supports the weight of the pump assembly. The weight of the power cable is also supported by the tubing through the straps which secure the power cable to the tubing. The well fluid is produced through the tubing to the surface.
Periodically, the pump assembly must be pulled to the surface for replacement or maintenance. Also, the well may require maintenance. This requires a pulling unit which will unscrew and pull the sections of production tubing from the well. Pulling the pump and putting it back into the well on the sections of tubing can be time consuming. It also requires a unit which has a draw works for pulling the production tubing.
Another method of deploying a submersible pump is on coiled tubing. A power cable extends through the coiled tubing for supplying electrical power to the pump assembly. The cable has an outer diameter that is less than the inner diameter of the coiled tubing, resulting in a cable annulus surrounding the cable. Standoff means extend within the cable annulus for frictionally or mechanically engaging the cable with the coiled tubing to support the weight of the cable with the tubing.
When an electrical submersible pump or other equipment is deployed using coiled tubing in applications where there is high sand production in the tubing annulus, there is a high risk that when production is shut off prior to pulling the equipment, the sand will settle to the bottom and stick the equipment in the hole.
Previous attempts have been made to stir up the sand to facilitate pulling the equipment. For example, U.S. Pat. No. 3,020,957 to Tausch teaches pumping fluids down the annulus and up the coiled tubing to remove sand. U.S. Pat. No. 5,040,598 to Pleasants teaches forcing fluids down coiled tubing and discharging the fluid against the wall of the wellbore and the fishing neck of the operating tool to clean the wellbore and fishing neck. The fluid is forced down the tubing to move sand around prior to connecting the tool to expose the fishing neck of the downhole tools to increase ease of attachment.
In this invention, the electrical submersible pump assembly is supported on coiled or continuous tubing. The cable extends through the coiled tubing for supplying electrical power to the pump assembly. The cable has an outer diameter that is less than the inner diameter of the tubing, resulting in a cable annulus surrounding the cable. Standoff means extend in the cable annulus for frictionally or mechanically engaging the cable with the coiled tubing to support the weight of the cable with the tubing. Preferably, the cable annulus serves as a flow passage for circulating cooling or lubricating fluid from the surface.
A tubing annulus is defined by an exterior of the coiled tubing and an interior of the casing or liner. Preferably, the production from the pump flows around the exterior of the coiled tubing and up the tubing annulus to the surface. A packer or polished bore is adapted to be set in the tubing annulus for sealing a lower portion of the downhole electrical submersible pump assembly.
A port is provided in the coiled tubing at the electrical submersible pump assembly for discharging fluid pumped from the surface down the cable annulus. A tube may be provided to extend downward from the port alongside of the electrical submersible pump. Fluid may be pumped from an upper end of the well down the coiled tubing/cable annulus and out of the port to free up sand accumulation around the packer. The fluid may be a gas, such as nitrogen, which is blown out of the port into the annulus as close to the packer as possible. Forcing gas into the annulus at this point will loosen up the sand and allow the unit to be pulled.
Standoff members, such as welded dimples for supporting blocks attached to the cable or spring supports that are attached to the cable, are provided to support the cable within the coiled tubing. The standoff members allow fluids to pass. The cable annulus and standoff members allow fluid, such as gas, to be forced down the well in a unique and advantageous method of unsticking downhole equipment in sandy applications prior to pulling the unit.